The Outer Drive Bridge, also known as the Link Bridge, is a double-deck

bascule bridge A bascule bridge (also referred to as a drawbridge or a lifting bridge) is a moveable bridge with a counterweight that continuously balances a span, or leaf, throughout its upward swing to provide clearance for boat traffic. It may be single- o ...

carrying DuSable Lake Shore Drive across the

Chicago River The Chicago River is a system of rivers and canals with a combined length of that runs through the city of Chicago, including its center (the Chicago Loop). The river is one of the reasons for Chicago's geographic importance: the related Chic ...

Chicago Chicago is the List of municipalities in Illinois, most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 United States census, 2020 census, it is the List of Unite ...

, Illinois, United States. Construction was started in 1929 and was completed in 1937 as one of the

Public Works Administration The Public Works Administration (PWA), part of the New Deal of 1933, was a large-scale public works construction agency in the United States headed by United States Secretary of the Interior, Secretary of the Interior Harold L. Ickes. It was ...

's infrastructure projects in Chicago. Completion of the bridge tied the north and south sections of the "outer" shore roadway, now called DuSable Lake Shore Drive, together. The bridge was officially named the Franklin Delano Roosevelt Memorial Bridge in 1982 to honor the centennial anniversary of the birth of

Franklin Delano Roosevelt Franklin Delano Roosevelt (January 30, 1882April 12, 1945), also known as FDR, was the 32nd president of the United States, serving from 1933 until his death in 1945. He is the longest-serving U.S. president, and the only one to have served ...

. It was planned by the Chicago Plan Commission, using Hugh E. Young as the consulting engineer, was designed by the Strauss Engineering Company, built by the American Bridge Company, and erected by Ketler and Elliot Company. It crosses near the mouth of the Chicago River.

Significance/purpose

This

bridge A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...

, a public works project during the

Great Depression The Great Depression was a severe global economic downturn from 1929 to 1939. The period was characterized by high rates of unemployment and poverty, drastic reductions in industrial production and international trade, and widespread bank and ...

, was designed to ease traffic flow on Michigan Avenue and in the Loop. At its completion in 1937, the structure was touted as the longest, widest, and heaviest

in the world. The Outer Drive itself, now known as DuSable Lake Shore Drive, links the south side to the north side of the city, running along the western shore of

Lake Michigan Lake Michigan ( ) is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume () and depth () after Lake Superior and the third-largest by surface area (), after Lake Superior and Lake Huron. To the ...

. It extends from its origin in Jackson Park on the South Side of the city to the Loop, across this Outer Drive Bridge over the

, to its eventual terminus at Hollywood Avenue and Sheridan Road in Edgewater on the city's North Side.

Funds

While the completion of the Outer Drive was considered one of the most important projects in the PWA it took many years to complete. A main issue was

funding Funding is the act of providing resources to finance a need, program, or project. While this is usually in the form of money, it can also take the form of effort or time from an organization or company. Generally, this word is used when a firm use ...

. Due to a lack of provided security by Chicago Park Districts, the allotment for the bridge was revoked until the districts were all in position to comply. The total cost of the Outer Drive is estimated at $11,563,000.

Economic justification

Calculations based on a

traffic flow In transportation engineering, traffic flow is the study of interactions between travellers (including pedestrians, cyclists, drivers, and their vehicles) and infrastructure (including highways, signage, and traffic control devices), with the ai ...

of 40,000 vehicles per day on a saving of eight minutes between Oak Street and Seventh Street, made possible by the use of the bridge rather than Michigan Avenue. The delay cost estimated to be one cent per car per minute (60 cents per hour for the value of time or the value of fuel saved) resulted in a savings in vehicle operation of $584,000 per annum; that amount capitalized at 5% would indicate that $23,360,000 could properly be spent to eliminate this delay, in the eyes of the decision makers at the time of the construction. From the perspective of engineering economics, this savings calculation justified the Outer Drive bridge project, showing a possible saving of $11,797,000.

Bridge operation

According to

Engineering News-Record The ''Engineering News-Record'' (widely known as ''ENR'') is an American weekly magazine that provides news, analysis, data and opinion for the construction industry worldwide. It is widely regarded as one of the construction industry's most au ...

, "Each leaf is to be operated by two sets of gear trains, consisting of four sets of gear reductions. Each gear train is connected to two 100-horsepower main operating motors, only one of which is to be used at a time. The time required for opening or closing the bridge against a wind is stated to be 57.6 seconds, of which 10 seconds is for

acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...

and 2.86 seconds for deceleration. The main operating racks are bolted to the underside of the outside trusses, the pitch radius being . The operating pinion, with a pitch diameter of , is mounted on a shaft of the gear train. Outer Drive Bridge Chicago - opened for sailboats 2011

Outer Drive Bridge Chicago - opened for sailboats 2011

Heavy locking devices are provided at the center of the bridge and at the rigid in its closed position. The center lock in addition to holding the leaves together in their closed position, also transmits live load shear from one leaf to the other. This center lock consists of a set of four female castings bolted to the river end of one leaf, and a second set of four male units bolted to the river end of the other leaf, all castings being on the centerlines of the trusses. The male unit consists of two castings forming a toggle. Heel or rear locks are necessary to prevent the leaves from opening when live loads pass over the part of the bridge between the trunnions and the rear break in the floor. Each leaf is provided with two pairs of rear locks, each pair being placed between the inside and outside trusses. The four locks of a leaf are connected by shafting, and operation by means of two 15-horsepower motors set either side of the centerline of the bridge" (April 22, 1937).

References

*"A Record Size Bascule," Engineering News-Record, v. 118 (April 22, 1937): 583-587. *"Chicago Gets Added PWA Funds for Outer Drive Completion," Engineering News-Record, v. 115 (December 5, 1935): 795-796. *"Continuous Girders Top Rigid Frame Viaduct Bents," Engineering News-Record, V. 118 (May 6, 1937): 671-673. *"Lakefront Boulevard Link Forms Milestone in Chicago Plan," Engineering News-Record, v. 118 (April 15, 1937): 546-548.

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